1. Technical Field of the Invention
The invention relates to photoprotective compositions comprising at least one aqueous phase, at least one water-soluble or water-dispersible polymer having a diblock structure A-B or a triblock structure B-A-B wherein A is an ionic water-soluble polymeric block and B is a hydrophobic polymeric block and at least one system screening out UV radiation, said screening system comprising at least one UV-A screening agent of the 4,4-diarylbutadiene type.
2. Description of Background and/or Related and/or Prior Art
It is well known that light radiation having wavelengths of between 280 nm and 400 nm allows tanning of the human epidermis, and that rays having wavelengths of between 280 nm and 320 nm, known by the name UV-B, cause erythemas and skin burns which can hamper the development of the natural tan; this UV-B radiation must therefore be screened out.
It is also known that UV-A rays having wavelengths of between 320 nm and 400 nm, which cause tanning of the skin, are capable of inducing its impairment, in particular in the case of a sensitive skin or a skin continually exposed to solar radiation. UV-A rays cause in particular a loss of elasticity of the skin and the appearance of wrinkles which lead to premature aging. They promote the onset of the erythematous reaction or amplify this reaction in some subjects and may even be responsible for phototoxic or photoallergic reactions. It is therefore desirable to also screen out UV-A radiation.
UV-A and UV-B rays must therefore be screened out and cosmetic compositions protecting the human epidermis, containing UV-A and UV-B screening agents currently exist.
These anti-sun compositions exist either in the form of an aqueous lotion or serum containing no fatty phase, or in the form of an emulsion of the oil-in-water type (that is to say a cosmetically and/or dermatologically acceptable carrier consisting of an aqueous dispersive continuous phase and a fatty dispersed discontinuous phase) or water-in-oil type (aqueous phase dispersed in a continuous fatty phase), which contain, in various concentrations, one or more fat-soluble conventional organic screening agents and/or water-soluble conventional organic screening agents capable of selectively absorbing harmful UV radiation, these screening agents (and their quantities) being selected according to the desired sun protection factor, the sun protection factor (SPF) being mathematically expressed by the ratio of the dose of UV radiation necessary to reach the erythermatogenic threshold with a UV-screening agent to the dose of UV radiation necessary to reach the erythermatogenic threshold without UV-screening agent. In such emulsions, the hydrophilic screening agents are present in the aqueous phase and the lipophilic screening agents are present in the fatty phase. Multiple emulsions also exist which are obtained after dispersing an invert emulsion in an aqueous phase.
There are known from EP-1,279,398 and EP-1,281,395 water-soluble or water-dispersible polymers, having a diblock structure A-B or triblock structure B-A-B, where A is an ionic water-soluble polymeric block and B a hydrophobic polymeric block, which are particularly advantageous because they exhibit gelling properties of water in low concentrations (less than 1%) and make it possible to stabilize surfactant-free emulsions, having nice textures.
These polymers can therefore be used in the following main galenic carriers:
(a) aqueous lotions or serums comprising no fatty phase, as gelling agents,
(b) emulsions which are dispersions of two immiscible liquids such as water and oil, as emulsifying and/or gelling agents. There can be distinguished direct emulsions comprising an oily phase dispersed in an aqueous phase, invert emulsions being dispersions of an aqueous phase in an oily phase. Multiple emulsions also exist which are obtained after dispersion of an invert emulsion in an aqueous phase.
The block polymers have the advantage of giving compositions having good safety towards the skin because they are free of small-sized surfactant molecules. They make it possible moreover, to obtain a broader range of textures than the commonly used gelling compounds (crosslinked hydrophilic polymers such as the Carbopols provided by Noveon, natural polymers such as xanthan gum) whose amphiphilic character is not sufficient to introduce contents of oil greater than 10%.
Among the available organic UV-A screening agents, a family of compounds which are particularly effective in UV-A is 1,4-benzene[di(3-methylidene-10-camphorsulfonic)] acid and its different salts, which is described in FR-A-2,528,420 and FR-A-2,639,347; they are indeed capable of absorbing ultraviolet rays having wavelengths of between 280 nm and 400 nm, with absorption maxima of between 320 nm and 400 nm, in particular in the region of 345 nm.
In the laboratories of the assignee hereof, it has been observed that the introduction of this type of UV-A-screening agent into sunscreening aqueous compositions gelled and/or stabilized with water-soluble or water-dispersible polymers, having a diblock structure A-B or a triblock structure B-A-B, can induce a reduction in their viscosity or their destabilization.
It thus appears necessary to have aqueous compositions based on water-soluble or water-dispersible polymers, having a diblock structure A-B or a triblock structure B-A-B which are stable in a broad range of possible consistencies and which can contain organic screening agents active in UV-A, of comparable efficacy to that of 1,4-benzene[di(3-methylidene-10-camphorsulfonic)] acid and its various salts without the disadvantages listed above.